Fuse having separate telescoping small current and large current arcing chambers



Aug. 30, 1966 R. E. FRINK 3,270,166

FUSE HAVI S RATE TELESCOPING SMA ENT AN A CURRENT ARCING CHAMB FiledSept. 30. 1963 5 heetsv-sheet l WITNESSES INVENTOR W fay/MM Russell EFrink ATTORNEY R. E. FRINK 3,270,166 ARATE TELESCOPING SMALL CURRENT GECURRENT ARCING CHAMBERS Aug. 30, 1966 FUSE HAA 5 Sheets-Sheet 2 FiledSept. 50, 1963 z g MM Aug. 30, 1966 R m 3,270,166

FUSE HAVING SEPARATE TELESCOPING SMALL CURRENT AND LARGE CURRENT ARCINGCHAMBERS Filed Sept. 30. 1963 5 SheetsSheer, l5

Fig.5A.

United States Patent 3,270,166 FUSE HAVING SEPARATE TELESCGPING SMALLCURRENT AND LARGE CURRENT ARCING CHAMBERS Russell E. Frink, ForestHills, Pa., assignor to Westinghouse Electric Corporation, EastPittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 30, 1963,Ser. No. 312,727 5 Claims. (Cl. 200-120) This invention relatesgenerally to fuse structures, and, more specifically, to fuse structuresadaptable to interrupt a relatively wide range of current values.

One object of this invention is to provide a novel type of highvoltagefuse which is relatively simple in construction and economical ofmanufacture, while being capable of efficiently interrupting relativelylarge currents.

Another object of the present invention is to provide an improvedhigh-voltage fuse in which the formation of corona during operation ofthe fuse is minimized to prevent the formation of deleterious acids,which could possibly prevent mechanical actuation of the fuse parts.

Still a further object of the present invention is to provide animproved fuse construction adaptable for selective operation, whereinrelatively low-current faults are interrupted within a small-bore fusechamber, whereas relatively high-current faults are caused to beinterrupted within a larger fuse chamber.

Still a further object of the present invention is to provide animproved fuse construction wherein highly efficient operation isachieved over a wide current range by a selective action being obtainedin designating in which of two fuse bores interrupting action isachieved.

Still a further object of the present invention is the provision of animproved high-voltage power fuse in which the coaction between theseveral fuse parts is such as to minimize the formation of corona.

Another object of the present invention is the provision of an improvedhigh-voltage fuse construction utilizing a tubular main arcing rodwhereby a better gradient of restored voltage is achieved by theparticular configuration of the movable fuse parts.

Still a further object of the present invention is the provision of animproved fuse structure having sufficient exhaust area to accommodatethe interruption of high currents, and wherein sufficient diameter andradius of the several parts is utilized to avoid the formation of coronaat high voltage.

An ancillary object of the present invention is the provision of animproved high-voltage fuse structure involving a pair of movableinterrupting assemblies, one of which is particularly adaptable forhigh-current interruption, and the other being adaptable for low-currentinterruption, and wherein a telescopic interrelation between such twointerrupting assemblies is provided to minimize the formation of coronaduring constant highvoltage operation of the fuse structure.

The particular fuse constructions disclosed in the present invention areparticularly applicable in utility and industrial high-voltage powersystems for protecting power transformers, feeder circuitsectionalizing, distribution transformers, high-voltage capacitors andpotential transformers. The voltage range may, for example, range from7.5 =k-v. to 13-8 kv., and higher, with a continuous current rating ofsay, for example, /2 ampere to 2100' amperes. Interrupting capacitiesmay range all the way up to 2,000,- 000 kva., and higher.

There are three very distinct problems existing is cirwit-interruptingstructures, such as, for example, fuse structure suitable forhigh-voltage and high-current application. Such problems involve coronaat high voltages, the ability to handle high currents, and the abilityto in- "ice terrupt low currents. These three problems areinterdependent, and as of the present time, no fuse manufacturer has thesolution.

The corona problem arises from the relatively small diameter of thearcing rods necessary in conventional designs of the prior art. Forexample, the formula for determining the corona starting voltage, asarrived by experimental investigation, is given by the followingformula:

e =21.1M0r6lnS/r (kv. to neutral) where M0 is the roughness factor andcannot exceed 1.

r is the radius of the conductor in cm.

5 is the relative air density and is 1 for standard conditions. S isphase spacing in cm.

Applying this formula to the dimensions commonly used for fuses showsthat fuses above '69 kv. having 4 inch diameter arcing rods will operatewith continual corona on the rod. The corona oxidizes the nitrogen inthe air and these oxides combine with moisture to form nitrous andnitric acids which attach and corrode the internal parts of the fuse.When this condition has progressed far enough, the fuse element maymelt, but the arcing rod will not withdraw through the fuse bore and afailure result. Serious field trouble has resulted from this cause.Furthermore, the problem does not yield itself readily to shieldingbecause of restored voltage distribution on interruption.

The second problem concerns the ability to accommodate high currents.The following approximate relations hold. Gas evolution per unit area isproportional to are current. Voltage interrupting capacity isproportional to the length of arc. Exhaust area is proportional to thesquare of the bore diameter. It follows that:

where:

Q is quantity of gas evolution, i is the current,

d is bore diameter,

1 is length of bore,

and

where Vis the velocity of gas exhaust. However, V" cannot exceed sonicvelocity, and l is determined by the required voltage interruptingcapacity. It follows that i can be increased until this velocity isapproached, and beyond this point the pressure will rise until the tubeis ruptured. The other alternate is to increase d to accommodate largercurrents.

From the above, it is seen that a larger diameter arcing rod is requiredto avoid corona, and a large bore is necessary for high currents, but alarge bore will not clear low currents since the arc diameter is toosmall to maintain intimate contact with the gas-evolving material. Anexperimental fuse with a /8 inch diameter arcing rod cleared top powerin a high power laboratory at 44 kv., 66 kv., and 72 kv., but it wouldnot clear 2000 amperes. The low-current problem was solved long ago inthe type BA400 fuse, manufactured by the assignee of the instantapplication, with the use of an auxiliary bore containing a small cableand wire which separate after an appreciable separation of the lowerterminal and the arcing rod, as shown in Rawlins U.S. Patent 1,976,634.For low currents, the cable and wire arrangement of the aforesaid patentshunts the current from the main gap, and when they separate, an arc isdrawn and interrupted in the small bore. If the current is large, thehigh are voltage generated in the small bore causes the arc to restrikein the large bore, and interruption takes place in the same manner as ifthe auxiliary bore were not used. However, tests show that corona on thesmall diameter cable and wire prevents this arrangement from being usedon fuses for the higher voltages. At present, it is desired to producefuses for voltages through 138 kv., and higher, and with interruptingcapacities of 2,000 mva., or more.

Accordingly, it is a further object of the present invention to providean improved highly efficient fuse structure adaptable for constantservice over long periods of time without suffering any disadvantage byvirtue of the fact that it is utilized at high voltage, and also whereinregardless of the time element, fast operation is always achieved, in aselective manner, to highly effectively interrupt either low-currentfaults or high-current faults.

The particular fuse construction of the present invention isparticularly suitable for dropout action in a manner as set forth inUnited States Patent 2,403,121, issued July 2, 1946, to Herbert L.Rawlins and John J. Mikos, and assigned to the assignee of the instantapplication.

Further objects and advantages will readily become apparent upon readingthe following specification, taken in conjunction with the drawings, inwhich:

FIGURE 1 illustrates, in perspective, a side elevational view of ahigh-voltage fuse structure embodying the principles of the presentinvention, and shown in the closed operative position;

FIG. 2 illustrates a longitudinal sectional view taken through the fuseelement of FIG. 1 with the fuse end fittings removed;

FIG. 3 illustrates, to an enlarged scale, the internal structure of thefuse device of FIG. 2 to more clearly illustrate the parts, again thefuse elements being shown in their intact condition;

FIGS. 3A and 3B are fragmentary views illustrating respectivelylow-current operation and high-current operation;

FIG. 4 is a sectional view taken substantially along the line IV-IV ofFIG. 3;

FIG. 5 is a vertical sectional view, taken to a somewhat larger scale,of a modified-type of fuse structure embodying the principles of thepresent invention;

FIG. 5A is a fragmentary view illustrating arc elongation in a fusestructure of the type illustrated in FIG. 5; and

FIGS. 6 and 7 are somewhat diagrammatic views illustrating the improvedelectrostatic conditions resulting from an application of the featuresof the present invention.

Referring to the drawings, and more particularly to FIG. 1 thereof, thereference numeral 1 generally designates a high-voltage high-powerdropout type of fuse structure, the general arrangement of which is setforth in the aforesaid Patent 2,403,121 Rawlins et al. As shown, thefuse structure 1 includes a base 2 formed of sheet metal, and a pair ofoutwardly-extending insulator supports 3, 4. The upper insulator support3 serves to support fixedly in position a break jaw 5, the details ofwhich are shown in FIG. 1 of the aforesaid patent.

Supported from the lower insulator support 4 is a hinge jaw 6, whichpivotally supports a fuse unit 7, interiorly of which extends fusibleelements, more fully described hereinafter. As shown in FIG. 1, the fuseunit 7 serves to electrically bridge the break jaw contact 5 and thehinge jaw contact 6 so that current will pass therebetween by way ofterminal pads 8, 9, to which the external circuit L L is connected.

The fuse unit 7 generally comprises a replaceable fuse structure 10,more clearly shown in FIG. 2, and a pair of end fuse fittings 11, 12.The upper end fuse fitting 11 comprises an operating eye, 11a and is, aswell-known by those skilled in the art, utilized for effecting openingand closing movement of the fuse unit 7 by means of a conventionalhook-stick, not shown.

The lower fuse fitting 12 comprises a hinge lifting eye, 12a which maybe employed in conjunction with the aforesaid switch-stick to effectphysical removal of the fuse unit 7 from the hinge jaw contact 6 forreplacement of the fuse unit 7.

With reference to FIG. 2 of the drawings, it will be noted that the fusestructure 10 comprises a fuse tube 13 of insulating material, such asfiber, synthetic resin or the like, and the opposite ends of the fusetube 13 are adapted to be closed by end terminal caps, or fuse ferrules14, 15, as well-known by those skilled in the art. The fuse ferrules 14,15 may be rolled into indentations 13a of the fuse tube 13, and securelyfastened into position by staking pins, so that the end fitting 11, 12when encircling the ferrules 14, 15 and clamped into position willsecurely engage the fuse-tube structure Without loosening.

With reference to FIG. 2 of the drawings, it will be observed that,generally, there are three sections to the fuse-tube structure, namelysections A, B and C. The fuse section A indicates the location of thefusible elements 16, which will fuse during operation of the fuse 1. Thefuse section B indicates the location of the interrupting arc passages,more fully described hereinafter, involving stacked blocks ofgas-evolving material 17, and the fuse section C relates to thebiasing-spring section of the fuse structure 10 to bias an arcing rodtoward its separated position, as explained more fully hereinafter.

With reference to FIG. 3 of the drawings, it will be noted that a coronatube 18 is soldered, or otherwise securely fastened, to the end of thefuse ferrule 15 and has brazed thereto, for example, a contact block 19.The right-hand end 18a of the corona tube 18, as viewed in FIG. 3 isbent radially inwardly to grade the electrostatic field during fuserupture, and thereby prevent a concentration of voltage stress resultingfrom the recovery voltage transient. Additionally, it will be noted thatthe right-hand end of the corona tube 18:: fixedly secures into place anorifice plug 20 having an orifice opening 21 therethrough. Extendingadjacent the opening 21 of the orifice plug 20 is a movable tubular mainarcing rod 22 having a cap portion 23 and threadedly secured, as at 24,to an unlatching extension rod 25. As set forth in the aforesaid Rawlinset al. Patent 2,403,121, during fuse operation, the extension rod 25projects externally of the fuse structure 10 to unlatch a dropoutbiasing mechanism enclosed in the hood 5a of the upper break jaw contact5 to effect thereby dropout action of the fuse unit 7.

A tension helical operating spring 26 is provided to bias the maintubular arcing rod 22 toward the right, as viewed in FIGS. 2 and 3,toward a circuit-opening position. During normal operation of the fusestructure 1, the tension spring 26 is extended, and is under tension.Upon rupture of the fuse elements 16, the tension spring 26 will beeffective to withdraw the main arcing rod 22 through the annular bore 27defined by the apertured gasevolving blocks 17 and a relativelystationary inner tubular gas-evolving rod 28. The evolution of gas bythe members 17, '28 will be effective to effect an expulsive blastaction forcing gas flow longitudinally of the established arc and outthrough the orifice opening 21 of the orifice plug 20.

It will be noted that the fusible elements 16 are attached at one end tothe extremity 22a of the main arcing rod 22, whereas the other, orleft-hand ends of the fusible elements 16, as viewed in FIG. 3, aresecured to a contact block 22 secured, for instance, by a plurality ofbolts 30, to the contact block 19 and also to the fuse tube 13 itself.

The contact block 29 is provided with an end portion 29a, which isdrilled and tapped to threadedly receive the threaded end 28a of therelatively stationary tubular gasevolving rod 28. Moreover, a conductingfuse cable 31 is electrically connected, as by a bolt 32, to the contactblock 29 and hence through the corona tube 18 to the end fuse ferrule15.

Making contacting engagement for a several inches of axial length of thefuse cable 31 is a relatively smalldiameter fuse wire 34, which isattached to the cap portion 23 of the main tubular arcing rod 22.

Encompassing the helical operating spring 26 is a metallic tube springshunt 35, which provides a friction stop 36 to prevent rebound of thearcing rod 22 following opening movement of the same by the tensionspring 26. The left-hand end of the contact shunting tube 35 is slottedas at 35a, to form thereby a plurality of inwardlybent contact fingers,which bear against the top portion 23 of the arcing rod 22 to enablecurrent flow therebetween.

In order to bias the contact fingers 35a radially in- Wardly against thetop of the arcing rod 23, a tension garter spring 38 is utilized. Toprevent the establishment of corona from the sharp corners of thecontact fingers 35, preferably a corona shield 39 is used, which coactswith the tube 35 to perform an electrostatic shielding function.

Fuse operation The operation of the fuse unit 7 will now be described.Fusible elements '16 rnelt in response to overcurrent, and the operatingspring 26 is effective to move the main arcing tube 22 toward the right,as viewed in FIGS. 2 and 3, at a high rate of speed. For the first fewinches of travel, wire 34 is in contact with the cable 31, and if thecurrent is low, they will carry it for an instant until their endsseparate and draw an arc 50 in the bore 40 provided by the openingthrough the gas-evolving rod 28. By this time, the main arcing tube 22has moved far enough to withstand considerable voltage, and the arc isinterrupted within the small fuse bore, or fuse chamber 40. FIG. 3Aillustrates arc establishment and the relative position of the severalparts during such low-current interruption.

However, if the fuse operates on a heavy current, such as a high-currentfault current, the fuse cable 31 and the fuse wire 34 will fusecompletely almost simultaneously with the fusible elements 16, andbefore the main fuse tube 22 has inoved an appreciable distance. Thehigharc voltage in the relatively small fuse bore 40 causes the arc tostrike from the end 22a to the contact block 29 and to be interruptedwithin the annular space between the aperture blocks 17 and the innergas-evolving tube 28, as shown more clearly in FIG. 3B.

FIG. 5 illustrates a modified type of construction in which the innergas-evolving tubular rod 128 has a spiral groove 128a cut, or otherwiseformed, on the external surface thereof. The purpose of this groove 128ais to cause the arc to spiral around the rod and thus increase itslength as shown in FIG. 5A.

It will be readily apparent to those skilled in the art that certainadvantageous results are achieved by the aforesaid described fuseconstruction. Specifically, there is provided sufficient diameter inradius of the several conducting parts to avoid the formation of coronaat high voltage. There is also provided suificient exhaust area toaccommodate the high currents. The auxiliary bore 40 for low-currentinterruption is completely shielded against corona by being telescopedwithin the outer main tubular fuse rod 22, as shown. Additionally, thereis provided a better gradient of restored voltage due to the size of themoving elements, as described in more detail hereinafter.

There is a higher ratio of surface to volume of arcing space resultingin higher evolution of gas and better performance. To illustrate thispoint more specifically, an annular space between a 1% diameter bore.and a /1 diameter rod has a volume of .55 cubic inch per linear inch ofbore, and a surface exposed to arcing of 5.89 square inches per linearinch. The ratio is 10.7. The volume is equivalent to a 27/32 diametercylindrical bore, which has a surface of 2.65 square inches per linearinch, or a ratio of 4.8.

Finally, there is a wider range of equivalent performance because thearc will be restricted when its diameter becomes equal to the clearancebetween the blocks 17 and the inner rod 28 (128), but it can expand tocompletely fill the annular space 27 provided therebetween.

I have discovered that the diameter of the movable tubular arcing rod 22should not be less than /2 inch in diameter. If this criterion isfollowed, deleterious effects resulting from corona formation will notoccur even at the higher voltages at which the fuse structure may beoperated in service.

The following is an explanation of the increased ability of the fuse 1of this invention to withstand a higher restored voltage than prior-artfuses. In prior-art fuses it was necessary to use a small diameter fusebore to provide low-current interrupting ability, which consequentlynecessitated a small-diameter arcing rod. In the new fuse 1 of thisinvention, this is no longer necessary. When two conductors, spacedapart, have a potential difference between them, the voltage gradient atthe surface of the conductors varies inversely with the size of theconductors. An accurate field map of the fuses would be difficultbecause of the close proximity of insulating materials, and because ofthe 3 dimensional configuration. However, the principle is illustratedin FIGS. 6 and 7 of the drawings. Suppose an arcing rod 51 has a numberof flux lines i// terminating on its surface. Now suppose that the rod51 is replaced by a larger rod 52 shown in FIG. 7 and that the samenumber of flux lines terminate on its surface. It will be observed thatthe flux lines terminating on the surface of rod 51 are spaced much moreclosely together than they are when they terminate on rod 52. This meansthat the gradient next to the surface at rod 51 is higher than at thesurface of rod 52 with the same potential existing. The result is that abreakdown will be initiated between electrodes of the size illustratedin FIG. 6 at a lower voltage than would occur if the diameter of theelectrodes were increased as shown in FIG. 7. It will therefore, beapparent that because of the diameter of the tubular arcing rod 22, thesame functions, in effect, as an electrostatic shield in thecurrent-carrying, or intact condition of the fuse structure, shown inFIGS. 2 and 3 of the drawlngs. I

From the foregoing description of the invention it will be apparent thatthere is provided an improved fuse structure 1 particularly adaptablefor high-voltage operation and effective to minimize the formation ofcorona by employing relatively large-diameter conducting parts.Additionally, the telescopic arrangement between the two movable arcingassemblies 22, 31, 34 shields the inner assembly 31, 34 by the outer oneand enables the adaptation of such an auxiliary fuse wire construction31, 34 to the higher volt-ages.

Although there has been illustrated and described specific structures,it is to be clearly understood that the same were merely for the purposeof illustration, and that changes and modifications may readily be madetherein by those skilled in the art, without departing from the spiritand scope of the invention.

I claim as my invention:

1. In combination, an elongated insulating fuse tube having a pair ofspaced terminals disposed adjacent opposite ends thereof, interruptingmeans disposed interiorly of said fuse tube including means forming astationary annular gas-evolving fuse bore, conducting means disposedwithin the fuse tube electrically interconnecting said terminals andincluding a movable tubular arcing rod having an arcing portion at oneend thereof, means biasing said movable tubular arcing rod along theannular gas-evolving fuse bore, means holding the arcing rod in itsintact connecting position including fusible means connecting the arcingend of the arcing rod to one of said spaced fuse terminals, a stationarytubular filler rod extending within the movable tubular arcing rod,

means securing the last-named rod in position so that relative movementof said rods will occur, and separable low-current conducting meansdisposed interiorly of the stationary filler rod and arranged toseparate subsequent to initial opening movement of the tubular arcingrod.

2. A fuse structure including an elongated insulating fuse tube having apair of spaced terminals disposed at opposite ends thereof, one of thespaced terminals including a contact block having an axially extendingthreaded bore therein, relatively high-current interrupting meansextending between said terminals including means defining an annularfuse bore and a movable tubular arcing rod movable therein, meanselectrically connecting one end of the movable tubular arcing rod to oneof the spaced fuse terminals, fusible means electrically connecting theother end of the movable tubular arcing rod to the other spaced fuseterminal, relatively lowcurrent interrupting means extending betweensaid spaced fuse terminals including separable low-current conductingmeans and disposed interiorly of the movable tubular arcing rod, theseparable low-current conducting means including a stationary tubularfiller rod extending within the movable tubular arcing rod, the fillerrod having a threaded end in threaded engagement in the threaded bore inthe contact block, whereby fusion of said fusible means will effectseparation of said separable low-current conducting means subsequent toopening movement of the tubular arcing rod.

3. An elongated fuse-tube structure having a cylindrical gas-evolvinglining and having separate high-current interrupting means andlow-current interrupting means, the combination therewith of a contactblock near one end of the fuse tube, the contact block having an axiallyextending threaded bore therein, the high-current interrupting meansincluding a movable tubular arcing rod biased at one end to anopen-circuit position and mechanically held at the other end by fusiblemeans, the lowcurrent interrupting means including a stationary tubularfiller rod having a threaded end in threaded engagement in the threadedbore in the contact block and longitudinally-separable overlappingfusible elements disposed interiorly of the tubular filler rod andseparable only after opening movement of the movable tubular arcing rod,whereby low-current are drawal will occur between the separated fusibleelements of the low-current interrupting means after previous movementsof the movable tubular arcing rod.

4. A fuse structure including an elongated fuse tube having terminalmeans adjacent opposite ends thereof and a gasevolving inner surface anda longitudinallyextending tubular filler rod co-acting therewith todefine an annular fuse bore, a movable tubular arcing rod movable alongsaid annular fuse bore and mechanically held adjacent one end thereof byfusible means, said fusible means being connected to one of saidterminal means, biasing means biasing the movable tubular arcing rodtoward the other terminal means, a low-current interrupting meansdisposed interiorly of said tubular filler rod and includinglongitudinally-overlapping fusible elements separable only aftermovement of the movable tubular arcing rod, means electricallyconnecting said low-current interrupting means llIl electrical parallelwith the tubular arcing rod and said first-mentioned fusible meansbetween the two terminal means, said electrical connecting meansincluding a contact block adjacent said one terminal means andsupporting the tubular filler rod in fixed position, whereby initiallyfuse operation occurs by fusion of said fusible means, and high orlow-current interruption is selectively achieved in either said annularfuse bore or within the bore of the tubular filler rod.

5. A fuse according to claim 1 in which the separable low-currentconducting means is additionally characterized as including a wire andcable in normal electrical contact and slidable with respect to eachother.

References Cited by the Examiner UNITED STATES PATENTS 2,183,751 12/1939McMahon et al. 200-117 2,247,702 7/ 1941 Ramsey 2001 17 2,253,719 8/1941McMahon 200-120 2,567,768 9/1951 Fahnoe 200-120 2,917,605 12/1959 Fahnoe200120 BERNARD A. GILHEANY, Primary Examiner.

1. IN COMBINATION, AN ELONGATED INSULATING FUSE TUBE HAVING A PAIR OFSPACED TERMINALS DISPOSED ADJACENT OPPOSITE ENDS THEREOF, INTERRUPTINGMEANS DISPOSED INTERIORLY OF SAID FUSE TUBE INCLUDING MEANS FORMING ASTATIONARY ANNULAR GAS-EVOLVING FUSE BORE, CONDUCTING MEANS DISPOSEDWITHIN THE FUSE TUBE ELECTRICALLY INTERCONNECTING SAID TERMINALS ANDINCLUDING A MOVABLE TUBULAR ARCING ROD HAVING AN ARCING PORTION AT ONEEND THEREOF, MEANS BIASING SAID MOVABLE TUBULAR ARCING ROD ALONG THEANNULAR GAS-EVOLVING FUSE BORE, MEANS HOLDING THE ARCING ROD IN ITSINTACT CONNECTING POSITION INCLUDING FUSIBLE MEANS CONNECTING THE ARCINGEND OF THE ARCING ROD AT ONE OF SAID SPACED FUSE TERMINALS, A STATIONARYTUBULAR FILLER ROD EXTENDING WITHIN THE MOVABLE TUBULAR ARCING ROD,MEANS SECURING THE LAST-NAMED ROD IN POSITION SO THAT RELATIVE MOVEMENTOF SAID RODS WILL OCCUR, SAID SEPARABLE LOW-CURRENT CONDUCTING MEANSDISPOSED INTERIORLY OF THE STATIONARY FILLER ROD AND ARRANGED TOSEPARATE SUBSEQUENT TO INITIAL OPENING MOVEMENT OF THE TUBULAR ARCINGROD.